Compared to the traditional printing, digital ink-jet printing had a lot of advantages such as low energy consumption, economize dye, clear patterns and so on, it also could satisfy the market's requirement such as individuation production, small batch production, and fast reaction. Therefore, at present, the digital ink-jet printing has attracted much attention. Direct-injection ink-jet printing, as one of the ink-jet printing method, is suitable for double-sided printing and single-sided printing respectively.
The cloth for double-sided clothing, silk broadcloth, reversible jacket and shirt, kerchief, banners and advertisement flags all need to be double-sided printed by ink-jet printing technology. We hope both sides of the double-sided printed fabric display the same patterns in shape, definition, color depth and colour saturation. Therefore, the pretreating agent used in double-sided permeation ink-jet printing process should help to transfer the ink from fabric's one side to another side and prevent the ink from spreading beyond the target printing area at the same time. However, there are still questions about double-sided permeation ink-jet printing using direct-injection ink-jet printing method. Ink always diffuse along the polyester fabric's longitude and latitude lines due to the low viscosity of the ink and the lack of hydrophilic groups on polyester fabric surface, which results in edge blurriness and poor definition. In order to solve these problems, the pretreatment of fabric prior to printing is crucial for the polyester fabric.
The research of double-sided permeation ink-jet printing of polyester fabric around the world focused on two aspects: (1) Application of alkali-treatment to turn polyester fabric into silk-like fabric. Just like the technique which created by Guan-xiu Jin and her partners, they used the mixed thickener EW-50, APS and resist S to treat the fabric which had been processed by alkali-treatment. Then transfer printing was carried out. By applying this kind of technique, the color depth of the reversed side of the fabric reached more than 75% of the front side, and the printing definition was more than 80%. CN01906712A showed an advanced production method of silk-imitation polyester fabric due to reducing amount of alkali, therefore, this technique can reduce sewage disposal and save raw material. But it's application was limited to some polyester fabric. (2) In addition to infiltrative colorant and thickener, penetrant were also added into the traditional printing color thick liquid for the flat screen printing or platform printing. For example, CN 104762832A published a method to make a kind of permeated print fabric by adding penetrated resin, bridging agent, chemical accelerant and dimethylformamide, and then the fabric was dried under specific move speed, temperature and pressure. Another example was CN 104562796A, which published a color paste formula containing penetrant. However, the fabric had a fishy smell due to introducing penetrant. At the same time, printing quality was poor due to the static electricity
The research of the pretreatment in order to enhancing the sharp definition of single-sided direct ink-jet printing mainly focused on 3 aspects: (1) Padding polymer on fabric's surface to weaken the fabric's penetrability. For example, CN101736606A published a technique that using β-cyclodextrin as pretreatment agent to increase the fabric's ability to embrace ink, which lead to improve the patterns definition. Yongping Lou researched the relationship beTween the types of thickener and polyester fabric's printing definition. Jinglan Yang researched the effect of methyl cellulose (CMC), sodium alginate, polyethylene glycol (PEG) and polyoxyethylene (PEO) on the printing sharpness of ink-jet printing. The PEG and PEO could obviously enhance the fixation rate of ink on the fabric's surface, but CMC and sodium alginate didn't have little effect on fixation rate. Nevertheless, more thickener and high polymer used could give a negative influence to the hand feeling of the printed fabric; (2) The polyester fabric was treated by catiomic reagent in cationic treatment process, this method used positive charges to attract the ink and enhance its fixation which could weak the penetrability. Just like the patent CN102071574A published a technique that used the quaternized chitosan as the pretreating agent to refine the fabric's ink print's definition and colour depth. It also made the fabrics antibacterial, But this method could only be applied on normal kind of dye typed fabric print; (3) Changing the polyester fabric's hydrophilic properties to improve its water-holding ability. For example, plasma technique and high energy ray irradiation technique were used to improve printing definition. But the requirements for equipment and operation were higher and it's not a cost-effective way, so it could not be used in a batch of polyester fabric processing work.